Carbon and nitrogen budget evaluation of natural and managed ecosystems.

摘要

Components of the annual carbon and nitrogen budgets were evaluated for a natural restored tallgrass prairie and fertilized and unfertilized, no-tillage and chisel plow corn agroecosystems for a four year period. The natural prairie and corn agroecosystems are located near Arlington, Wisconsin and reside on Plano silt loam soil (fine-silty, mixed, mesic Typic Argiudoll). Inorganic nitrogen and dissolved carbon leaching losses were quantified in-situ using equilibrium-tension lysimeters. Inorganic nitrogen leaching was a negligible component of the nitrogen balance for the natural prairie, however nitrogen leaching was a significant component of the nitrogen balance for the fertilized agroecosystems. Dissolved carbon leaching was greatest for the fertilized chisel plow agroecosystem and smallest for the natural prairie. Denitrification was assumed negligible for all ecosystems. However, large net nitrogen mineralization field measurements for the agroecosystems suggested that denitrification may be a significant export of nitrogen from the agroecosystems since leaching losses could not alone reconcile the differences between the inputs and outputs of nitrogen to the fertilized agroecosystems. Soil surface carbon dioxide emissions from the prairie were significantly higher than carbon dioxide emissions from the agroecosystems. High soil respiration fluxes contributed to the nature of the restored prairie being a net carbon source rather than a net carbon sink. Carbon leaching was a minor component of the carbon budgets for both the prairie and agroecosystems. Compared to the prairie, the fertilized agroecosystems were less efficient or leaky in terms of carbon assimilated per unit nitrogen leached. Computer modeling of soil biogeochemical cycling complemented field measurements and provided valuable insight into the mechanisms contributing to and controlling such important processes as nitrate leaching from the rooting zone of fertilized crops.